Anatomy of the Ventilator Dean Hess PhD RRT Associate Professor of Anesthesia Harvard Medical School Assistant Director of Respiratory Care Massachusetts General Hospital Editor in Chief Respiratory Care
air O 2 filter filter PATIENT Microprocessor (mode and breath delivery) inspiratory valve(s) (flow, volume, pressure, F I O 2 ) expiratory valve (PEEP) humidifier electrical power atmosphere monitors & alarms
expired gas humidifier ventilator patient Aerosolized drug (nebulizer or MDI) filter dead space gas compression bias flow suction
Both nebulizers and MDIs can be used to deliver Beta 2 -agonists to mechanically ventilated patients.
Careful attention to details of the technique employed for administering drugs by MDI or nebulizer to mechanically ventilated patients is critical, since multiple technical factors may have clinically important effects on the efficiency of aerosol delivery.
Flow (volume) varies with lung mechanics and patient effort
time Volume (mL) Pressure (cm H 2 O) Flow (L/min)
Equation of Motion Volume Ventilation E = 1/C X X P MUS + P AW = E V + R V . fixed volume and flow increased effort decreased airway pressure fixed pressure increased effort increased flow and tidal volume P MUS + P AW = E V + R V . Pressure Ventilation
Lack of a back-up rate and wakefulness drive leads to central apnea and sleep fragmentation
Parthasarathy, Am J Respir Crit Care Med 2002; 166:1423 Apneas per Hour
Volume-Control vs Pressure Control Evidence for better outcomes with either volume-control or pressure-control is lacking VCV PCV PSV Tidal volume Fixed Variable Variable Inspiratory flow Fixed Variable Variable Airway pressure Variable Fixed Fixed Inspiratory time Fixed Fixed Variable Rate Minimum set Minimum set Not set